Modelling and verification for dual time-dependent chloride diffusion of circular concrete columns in marine environment

A dual time-dependent chloride diffusion model (DTC) for circular concrete columns in a marine environment was proposed by considering the time dependency of chloride diffusion coefficient (D) and surface chloride concentration (Cs). The partial differential equation (PDF) describing the time-dependent chloride diffusion in circular concrete columns was established in the polar coordinate system firstly. Then Duhamel's theorem, variable separation method and the properties of the Bessel function were adopted to solve the PDF and to develop the DTC for circular concrete columns. Finally, the accuracy and applicability of the DTC for circular concrete columns were verified by natural diffusion tests and finite element method. The results indicated that the larger the radius of the circular concrete columns is, the lower the chloride concentration will be, and the difference in chloride concentration distribution in circular concrete columns caused by the change of radius becomes more significant with the exposure time. The chloride concentration would be overestimated if the time-dependent behavior of D or Cs were ignored. Furthermore, the effect of the time dependency of D on the chloride diffusion is more significant than that of Cs. The proposed model is applicable for various time-dependent function forms (e.g., reciprocal, exponential, power and logarithmic functions) of Cs with good applicability.